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rocker arm upgrade ?

This is a discussion on rocker arm upgrade ? within the Internal Engine forums, part of the LSx Technical Help Section category; allright well i have a ms4 cam, prc double springs, and i am getting ready to get the prc ls6 ...

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    rocker arm upgrade ?

    allright well i have a ms4 cam, prc double springs, and i am getting ready to get the prc ls6 heads offered by tsp, i want to change out the rocker arms while im at it, but dont know what kind of rocker arms to get. any help would be great. thanks.

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    Senior Member mrr23's Avatar
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    dark bowling green
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    the crane accelerated lift rockers.

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    that would be best for my cam and other mods?

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    Senior Member mrr23's Avatar
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    best meaning ratio? well 1.7 is stock. if the springs can handle it and you have proper piston to valve clearance, then go 1.8.

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    thats the thing, after the cam install i have been having a lot of ticking noise. i had a rocker arm explode on me when i was driving down the road, so i replaced it and the noise went away, but started back up. i checked everything and it was all good. i think its piston slap, so im not sure how good my ptv clearance is. the springs are prc double springs that are rated to .660 lift so i think they could handle 1.8 ratio.

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    Senior Member mrr23's Avatar
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    well, to check the piston to valve clearance, you would have to pull a head and put clay on the piston. reintall the head, turn the motor over by hand, pull the head, measure how much the clay was compressed, then go from there.

    safe bet is stay with the 1.7 ratio. if you want to do all of that work, then go for it.

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    allright well where can i get some info on the crane accelerated lift rockers?

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    Senior Member mrr23's Avatar
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    http://www.cranecams.com/index.php?s...lvl=3&prt=2059
    some info there.

    here's a better explanation from vinci

    Quote Originally Posted by vinci website
    Here are a couple of questions about our rockers we would like to address.

    Does the varying rocker ratio adversely affect spring harmonics?
    Wouldn’t a fixed ratio rocker be easier on the valve train and cause fewer problems?
    The first point that needs to be made in answering these questions is that there is no such thing as a constant ratio rocker arm unless you are talking about a very limited range of lift (.150” or less). This is because the pushrod seat end of the rocker and the valve tip end of the rocker are operating through two different distances and their ratio must constantly vary. Traditionally, most rockers have been designed to start the valve off the seat and return it to the seat slowly. (i.e. traditional SBC 1.5 ratio rockers started the valve off the seat at a ratio of 1.4 and did not get to a 1.5 ratio until .350” valve lift). This was because many OE valves were made in two pieces, and quick opening and closing rates could compromise the valve. The use of high quality, one-piece valves has made this a non-issue. Many performance aftermarket companies, including Crane, tried to develop rockers that were as close to constant ratio as possible. For instance, many 1.6 ratio rockers bring the valve off the seat at 1.62; by .250” valve lift, the ratio increases to 1.65 and by .550” valve lift, the ratio comes back to 1.61. Again, the ratio is varying due to the different length of operating arcs of the end of the rocker. Crane’s “Quick-Lift” design causes an “advertised” 1.6 ratio rocker to start the valve off the seat at a ratio of 1.72 and bring the ratio back to 1.60 by .250-.300” net valve lift. This ratio is then maintained through the rest of the lift profile until the valve is within .250-.300” from going back on the seat. It is then returned to the seat at a ratio of 1.72. This geometry is illustrated in this diagram.

    Benefits of this geometry include more flow into the cylinder earlier in the cycle, quicker closing of the valve to trap cylinder pressure before combustion, more effective duration at .200” net valve lift while maintaining a relatively short seat-to-seat timing, and less valve spring seat pressure required because of the mechanical advantage of the higher seat ratio.

    During development testing and now corroborated by more than two years of field-testing in competition, we have not seen any indication that the “Quick-Lift” geometry contributes to any additional valvetrain problems in any way. In fact, the evidence so far shows that our “Quick-Lift” Polymer Matrix Composite Bearing Shaft Mount Rockers actually seem to reduce harmonic issues in the valve train and extend spring life. At this time, we have no way of telling if this is the bearing construction or the geometry of the body or both! One other important feature of these rockers is the absence of needle bearings, which can break loose under extreme valve spring pressures and cause catastrophic engine problems. On average, we have eliminated 544 needle bearings from an engine with this design!!

    “Quick-Lift” rocker body geometry causes the rocker arm to be a dynamic component in the opening and closing rate of the valve. Some people who don’t seem to understand this think it is “unnatural” to cause the valve to open faster than the cam lobe dictates, but OHC designs with finger followers have been doing it for years. After all, aren’t we interested in what the valve is doing relative to the piston position? Who cares how we get the valve there at the right time? The point is that “Quick-Lift” rocker geometry will broaden the torque curve (torque x RPM/ 5252 = HP!!!) of any cam you use it with. Our only warning: Super Stockers and others running extremely tight piston-to-valve clearance should check this with “Quick-Lift” rockers. Try ‘em; we know you’ll love ‘em!!

    VHP and Crane Cams have been working with each other for many years. Together, we have strived to provide the very best products we can with the latest technology available. We think, we design, we manufacture, we test....then we market the product. It seems that there has been much confusion about Crane/Vinci "Quick-Lift" cam lobes and "Quick-Lift" rocker bodies. We claim that the use of the Quick-Lift lobes with the Quick-Lift rocker bodies results in "effective valve lift" durations @ .200" valve lift equal to most other cam/rocker combinations using cams with 4-8* more duration at .050" cam lift. This is the result of the Quick-Lift Rocker body design. We do not state that our cam lobes (by themselves) give this advantage. The same laws of physics that limit every other cam designer limit our cam lobe designs. We attribute the advantage in valve lift to the "translation" properties of the varying ratio design of our Quick-Lift rocker body design. If you don’t believe us, test any cam lobe (Crane, Comp, Cam Motion, etc.) with stock LS1 rockers. Install a dial indicator on the retainer and a degree wheel on the crank. Plot a lift vs. degrees of rotation curve. Then install the Crane LS1 1.7 rockers (with the pushrods in the Crane kit) and plot the same curve. Measure the duration at .200" net valve lift. The Crane rockers will definitely provide more duration at this checking point. The reason for this is that, contrary to popular belief, the stock LS1 rockers are only 1.7 ratio above .480" valve lift. They actually start the valve off the seat at a 1.54 ratio. What do you think that ratio does to a "super fast" cam lobe? Slows it down quite a bit? The Crane rockers, properly installed, bring the valve off the seat at 1.79. Doesn’t take a math wiz here to see what combination is going to get open quicker and longer!! If you really want to see something interesting, take two lobes that have identical .050" seat-to-seat timing, identical .200" lifter rise timing, but one provides .583" valve lift with 1.7 ratio and the other providing .551 lift with 1.7 ratio. Plot a lift vs. duration curve with any rocker you want (other than Crane) and measure the duration at .200" valve lift. Then do a plot of the .551 cam with 1.8 Crane rockers (this will net out .583 also) and measure the duration difference at .200" valve lift. You will be impressed by how much more this second plot gives over the first. It’s also quicker on the drag strip! We’ve done this. Every person reading these threads can do something like this.

    Our point is that the only thing that counts is what happens at the valve and the overall rocker ratio is fundamental to this. Contrary to popular belief, there are no fixed ratio rockers on the market (this is because the valve tip end and pushrod seat end operate on two distinctly different arcs). This is why some rockers add power and some don’t. Crane/Vinci have elected to do extensive development with rockers as a supplement to the lobe. The quickest lobe in the world doesn’t mean diddly if you are using slow acting rockers! Like everything else, it’s the combination that counts. FYI, the higher opening and closing ratios actually allow lower seat pressures because the mechanical advantage of the ratio helps maintain proper lifter preload! Check it out. This isn’t smoke and mirrors; it’s applied geometry and it works!! Roger Vinci


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    wow thanks man.

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    Senior Member mrr23's Avatar
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    no problem

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    Nitrous Tuner LS2Tuner's Avatar
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    YOU ALSO NEED TO CHECK THE LIFTER PRE-LOAD!!!!
    Most aftermarket cams are smaller base circles than stock.= Which means your stock length pushrods are NO longer the right length.
    For the money the YellaTerras are not a bad choice eighther.
    Don't be afraid of the bottle!!! Be afraid of your tune!!!

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    Senior Member mrr23's Avatar
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    if he gets the cranes, they are fully adjustable. they come as a kit. rockers, locks, 7.250 hardened pushrods (shorter required), screw-in-studs, and guideplates.

    if staying with a non adjustable rocker, then getting a pushrod length checker is essential as well. that way, you can get the correct length pushrods.

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    what do you guys think of the comp cams pro-magnum roller rocker arm kit.? i can get it for about $500 and it comes with everything.

  14. #14
    Senior Member mrr23's Avatar
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    nice rockers.

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    allright cool. thats what ill probably be getting.

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    Harland Sharps FTMFW!!!!

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